The transistor is an important building block of electronic devices and has been widely used in the development of various sensors, including electrical and chemical sensors. Among the different types of transistor based sensors, electrochemical transistors (ECTs) have gained particular attentions for their simple and low-cost fabrication, mechanical flexibility and also the adaptability to miniaturization, in contrast to the traditional transistors such as field effect transistors (FETs). Organic materials such as conducting polymers have been used to develop organic electrochemical transistors (OECTs), which facilitate the use of OECTs in the biological and chemical sensing areas.
In contrast to field effect transistors (FETs), in which the detecting mechanism is field driven, i.e., the density of charge carriers between the source and the drain terminals are modulated via capacitive coupling between the gate electrode and the transistor channel, the detecting mechanism of the organic electrochemical transistors (OECTs) is potential driven, i.e., based on electrochemical redox reactions between an electrolyte and the organic electrodes. The switching between an oxidized state and a reduced state during the electrochemical reaction corresponds to a change of conductivity of the transistor, and thereby facilitating the quantification of the analyte in the electrolyte. The operation of the OECTs in electrolytes enables the OECTs to be operable under relatively lower voltages, and thus allows the OECTs to be tailored to specialized applications such as for detection of biological molecules in the physiological environment.
The OECTs offer improved biological and mechanical compatibility when compared to the traditional electronic materials. Particularly, for biosensing applications, it is required that the devices are reliable, robust, miniaturized and inexpensive.
US2013128332 A1 describes an OECT made with multiple planar layers including a substrate, electrodes and a solidified electrolyte layer. US 20120247976 A1 also teaches an OECT made with planar substrates for glucose sensing. These planar OECTs possess practical disadvantages due to their relatively poor flexibility and bulkiness, which prevent them from being used in applications in which flexibility and small-scale operation are essential.
For providing better flexibility to the OECTs, G. Tarabella et la. (G. Tarabella, M. Villani, D. Calestani, R. Mosca, S. Iannotta, A. Zappettini and N. Coppede, J. Mater. Chem., 2012, 22, 23830) developed a cotton thread based OECT for the detection of saline in aqueous solution fabricated by a relatively simple process. X. Tao et la. (X. Tao, V. Koncar and C. Dufour, J. Electrochem. Soc., 2001, 158(5), H572-H577) has also reported the construction of a plastic multifilament based OECT for used in the textile industry.
It is therefore an object of the present invention to provide an organic electrochemical transistor device in which the aforesaid shortcomings are mitigated, or at least to provide a useful alternative.